Invasive weeds in the years and garden
I have a flood of PINELIA and LESSER CELANDINE. I want to exterminate the PINELIA from the garden. 20% vinegar only defoliates. The bulbs are 6 to 8 inches deep and are now as big as marbles. I want to stay chemical free. HELP! By the way, LESSER CELANDINE seems to be ROUNDUP resistant and now I am ROUNDUP resistant. LESSER CELANDINE, I understand, is also called Pilewort because of it's hemorrhoid resembling root structure.
Both of these weeds are very challenging to control, and you are correct that horticultural vinegar will only kill the top growth, not the root systems and bulbs. For the Pinellia ternata, you can use a digging tool and dig deep to remove the corm (bulb) that is attached to the stems. https://www.scottarboretum.org/pinellia-ternata/ The other option, yes, would be to use glyphosate. When applied directly onto actively growing foliage, it will translocate down to the roots to kill them. There are no organic options that are as effective for tough perennial weeds.
Lesser celandine is best controlled in early spring when the new foliage starts growing. For small infestations, the clumps can be dug out by hand, but you have to be very care about lifting out all of the very small tubers and take care not to spread them about in other areas of your landscape when you take the plant material to the trash. An herbicide is usually necessary to control large infestations and the best time for an herbicide application starts in February-March. See recommended manual and chemical removal options here, https://www.invasive.org/weedcd/pdfs/wgw/lessercelandine.pdf
Also, you might be interested in reading through our information about alternatives to glyphosate.
I heard a suggestion and I would like your opinion. I had suggested to me to cover the garden for a season with heavy black plastic, sealing all the edges to prevent ventilation beneath the plastic and hope that the sun will bake and sterilize the soil. The Pinelia corms go 6 to 8 inches deep. Could they bake and die?
Could I achieve a heat high enough to kill them?
We have no information that black plastic would be effective at that depth. However, leaving the plastic on for several seasons/years may work.
Incidentally, early fall is the best time to apply glyphosate to get it to translocate deeply to roots. Plants are pulling their resources down to the roots in preparation for winter, and will pull the glyphosate down more efficiently now. Leaves must still be green though when you apply it.